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%I #13 Jan 17 2020 05:38:23
%S 2,6,6,1,5,7,0,0,1,8,7,1,6,3,7,5,6,2,5,9,6,4,1,5,5,1,2,4,4,6,5,7,9,6,
%T 8,9,7,2,6,2,1,7,9,9,9,3,9,5,1,2,7,7,5,5,7,1,2,5,0,7,7,5,4,0,6,1,3,0,
%U 1,5,8,1,2,0,9,2,7,9,2,4,1,3,4,5,4,5,2,4,0,7,3,1,1,9,7,3,4,2,6,0,0,4,3,4
%N Decimal expansion of the two-dimensional series sum_{i,j=-infinity..infinity} (-1)^(i+j)/(i^2+(3*j+1)^2).
%H Steven R. Finch, <a href="http://arxiv.org/abs/2001.00578">Errata and Addenda to Mathematical Constants.</a> p. 8.
%F (2*Pi/9)*log(2*(sqrt(3) - 1)).
%e 0.2661570018716375625964155124465796897262179993951277557125...
%t RealDigits[(2*Pi/9)*Log[2*(Sqrt[3] - 1)], 10, 104] // First
%K nonn,cons,easy
%O 0,1
%A _Jean-François Alcover_, Aug 11 2014
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